It is known to produce shaped synthetic-resin bodies and particularly molded bodies of foamed synthetic resin, or bodies having a core or interior portion of foamed synthetic-resin material, by introducing the flowable synthetic-resin mass in a heated state into a mold consisting of a plurality of separable parts and defining a mold cavity of the desired shape. The mass of synthetic resin in the mold cavity is generally then precooled to cause initial setting or hardening, whereupon the body is ejected from the mold cavity (after opening of the mold). The body can then be finally cooled (finish cooled) under conditions assuring temperature homogenization throughout the cross section of the body, i.e. under tempering conditions.
Such systems have been found to be highly effective for the production of relatively massive bodies, such as articles of furniture, since they permit the removal of the initially set unit from the mold cavity before complete setting and hardening of the body, thereby making it unnecessary to retain the body in the mold for the full setting time and markedly increasing the cycling time of the injection-molding machine.
In the prior-art systems, the mold parts are generally cooled by the feeding of a coolant through passages formed in the mold parts. The injection can be effected by mechanical means, e.g. ejector pins or rods, or pneumatically.
A pneumatic ejector has been described in German Auslegeschrift DT-AS No. 23 24 215 and comprises a source of compressed air which is connected to nozzles which open into the mold cavity and are trained against the surfaces of the mold body therein to force the body out of the mold.
Such systems have been mentioned because the compressed air serving to eject the body has a minor cooling effect upon the body and this represents a form of direct-contact cooling between a gaseous coolant and the synthetic-resin material of the body.
However, this effect is minimal, as noted above, and compared to the conductive cooling effect brought about by the cooling of the mold parts, can be treated as insignificant.
Thus, in spite of the fact that the precooling techniques of the prior art enable the initially set and cooled body to be removed from the mold cavity prior to complete solidification and cooling of the body, the latter must remain in the mold cavity and in contact with the walls of the mold for a relatively long time.
In other words, the duration for which the molded mass must be retained in the mold cavity is determined, even in the case of pneumatic ejection, primarily by the rate at which the indirect cooling of the mold parts is able to conductively abstract (dissipate) heat from the synthetic-resin mass in contact with these parts. Since this duration is the determining factor of the cycling time or rate, the productivity of the injection-molding machine is restricted by the conventional cooling approach and, for a given required output rate of molded bodies, may result in the need for additional machines and high capital expenditure. Furthermore, the conventional systems, because of the thermal inertia of the mold, are of low energy efficiency to the extent that they rely primarily on cooling of the mold to effect the precooling of the molded body.